This invention relates to an error correction system for use in a packet exchange system which can transfer packets without the necessity of retransmitting of information, such as datum, a speech, and an image.
Heretofore, a packet exchange system of the type described is used for transferring a packet from a transmission end to a destination or reception end. In this event, information signals, such as a speech or voice signal and an image signal, are preceded by a packet header and are transmitted or conveyed by the packet in the packet exchange system which is operable in accordance with non-high level data link control procedure. The packet header is helpful to specify the destination reception end and the transmission end.
It is to be noted that no re-transmission is carried out in such a system and that the packet should be delivered to the destination reception end without failure. Otherwise, the information signals are undesirably sent to a wrong one of the reception ends. Therefore, correct transmission is required for the packet header as compared with transmission of the information signals, such as the speech and the image signals.
In general, it is known to use a Hamming code or a parity bit in connection with an information signal of a comparatively short data length of, for example, several bits. In this case, a single bit error or a double bit error is corrected by use of the Hamming code or addition of the parity bit when the information signal has a short data length, as mentioned before.
It is mentioned here that the packet header is usually composed of a long data length of, for example, several tens of bits. In addition, the packet exchange system is often used in very bad circumstances such that the packet header is subjected to the influence of noise. Taking this into account, a double error, a triple error or a t-tuple error more than the triple error very often takes place in the packet header and may be preferably corrected in each packet header.
Conventionally, consideration is however directed neither to the correction of the packet header nor to the correction of a double or a triple error.